The present invention relates to an apparatus for liquid-liquid extraction, i.e. extraction of a liquid from a mixture of multiple liquids, and a method of using such an apparatus. More particularly, the invention relates to an apparatus for liquid-liquid extraction in which counterflowing liquid phases are brought into contact with each other in an extraction column having rotating plates, with at least one of the plates being arranged at a non-zero angle with respect to a plane normal to a shaft of the column.
In general, liquid-liquid extraction achieves the isolation of a desired liquid from the multiple liquids of an initial mixture by introducing an additional liquid not present in the initial mixture and not soluble in the initial mixture, to form an aggregate mixture. The additional liquid, often a solvent, is appropriately selected such that it preferentially adheres to the desired liquid in the initial mixture and such that it is insoluble with the initial mixture, so that the aggregate mixture stratifies into two distinct liquid phases or layers, such as oil and water, when it is not agitated. The aggregate mixture is then acted upon such that its components are separated, when the agitation is afterward removed, which results in the separation of the multiple liquids of the initial mixture, the desired one now joined with the solvent. Efficient extraction involves equipment that agitates and thereby maximizes the interaction between the two liquid layers of the aggregate mixture being separated.
Prior art liquid-liquid extraction apparatuses and processes have included different configurations of propagating and rotating plates. Stationary trays, sometimes in combination with pulsating and reversing flows have also been utilized to aid in the separation of the components of the liquid phases being passed through the apparatus in either co-current or countercurrent flow. The prior art devices seek to separate compounds based on their relative solubilities in two different immiscible liquids, for example, water and an organic solvent.
However, some prior art apparatuses suffer from inefficiencies because the agitation provided to the aggregate mixture is insufficient to provide a high level of uniform distribution of the components within the aggregate mixture and efficient mass transfer of the liquids from their initial to their final compositions. Those apparatuses which can provide sufficient agitation are of complex and costly construction. Such apparatuses are also difficult to maintain as the components are very cumbersome and high-maintenance.
Earlier designs of extraction columns required the columns to be relatively large in order to provide sufficient height for reasonably efficient liquid extraction. Subsequent designs have utilized plates disposed along a shaft attached to propagating means, which has proved to be unreliable and difficult to upkeep.
In some prior art designs, a plurality of perforated plates are spaced along a shaft within an extraction column. The plates are each oriented perpendicularly to the shaft, and the shaft is propagated along its axis so that the plates interact with the aggregate mixture of multiple liquids introduced into the column. Not only are such devices required to be very large with some columns being over a hundred feet tall, the drive mechanism needed to propagate such heavy machinery can be very expensive and are often physically located high in the air and at the top of the column. The drive mechanism and the components themselves are taxed heavily and can suffer from fatigue or can break down after long term use. Frequent maintenance of such devices is commonly required and the high location of the drive mechanisms makes such maintenance difficult and costly.
Other prior art designs include a column having rotating paddle blades that, when rotated with the shaft, force the materials in lateral directions perpendicular to the axis of the shaft. These designs require larger columns of sufficient girth to support additional components. The liquid also flows inefficiently in a serpentine path and is exposed to a relatively smaller cross sectional area of the column due to its inefficient movement and interaction with multiple components required to induce such movement.
The present invention provides an improved apparatus and method for the liquid-liquid extraction process that overcomes deficiencies of the prior art devices . . . .